Question

The growth of the HPV was monitored as follows: 10⁹ cells and 10⁶ viruses in one milliliter were incubated under appropriate conditions. Following a first infectious cycle, a direct count and a plaque assay were performed. In the case of the direct count, the mixture was diluted by a factor of 1000X after which beads were added to obtain a final concentration of 1 X 10⁴ beads/mL. A microscopic field of vision revealed 20 beads and 150 virions. In the case of the plaque assay, 67 plaques were observed on a plate on which 0.1 mL of a 10^-5 dilution was assayed.

How many infectious cycles, including the first one, could be completed under the above described conditions?

Answer 1

The initial virus count = 10⁶ . Let this number of virus are present in 1 ml. The mixture was dilute by a factor of 1000x , which means the virus is diluted into 1000ml. 1000 ml of mixture contained 1,000,000 virus, 1 ml contained 1,000 virus, and 0.1 ml contain 100 virus.

After n number of replication cycles, there are 67 virus in 10^-5 dilution, which means 67 × 10⁵ virus are present in ol1 ml.

In 1 ml, there are 6.7 × 10⁷ virus

Therefore, 100 × 2ⁿ = 6.7 × 10⁷

n (number of generations) = number of infectious cycles = 19.35